Antenna system



Sept. 2, 1952 R. M. WILMoTTE ANTENNA SYSTEM 2 SHEETS-SHEET 1 Filed Dec. 12, 1946 INVENToR.

Raymond M Wi/moze sept. 2, 1952 Filed Deo. 12, 1946 /Fig-2 R. M. WILMOTTE ANTENNA SYSTEM 2 VSHEETS--SHEIET 2 xe E@ Mmmm msi

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Patented Sept. 2, 1952 A UNITED STATES enr ENT oFFIcE: "jf' ANTENNA SYSTEM Raymond M. Wlmotte, New York, N. Y., assignor to Padevco, Inc., WashingtomD. C., a corporation of Delaware Applicationnecemher 12, 1946, seria1:N0.v15,s5s

V claims. (o1. 25d-33.53)

L.This invention relates Ato an antenna system .for ,radio broadcasting stations transmitting pro- `vgrams on two different frequencies.

wusually, but not always, insulated steel towers. ..Generally the very high frequency antenna for FM or television .must be placed lat a height-I 'greater than that-of the steel towers in order to have `adequate coverage. The provision of an additional tower of lsuficient height for supporting the very 4high frequency antenna is eX- pensive and would ,disturb the radiation pattern Aofthe antenna .array if placed on the same plot "of ground.

`It is an object of this invention to mount the very high frequency antenna at a suitable height without upsetting the radiation pattern of the AM antenna array.

Another object of my `invention is to mount a "very high frequency .antenna at a suitable `height and without requiring additional land area.

rThe invention will be understood from the following description and from the drawing:` in

2 L radiationpattern required. The system as kso' Afar described is conventional. f

On one of the antenna towers, for example2, a superstructure II is erected. The superstructure lIis supported on the tower 2 by insulators I3. A very-high frequency l antenna 1I2, is mounted at the top of structure Il. -A suitable transmission line I5 connects the antenna.,|2 'to a very high frequency transmitter v(not shown). The transmission line l5 may belaicoax'ial transmission line or may Vconsist of conductors inside of aconduit, as shown in the application .of.L.

. Sanson, .525.079, sied March 4, 1944.,nmrPaternav #2,441,086 issued May 4, 1948.

The structure l I has a heightsuicient--to -raise the very high frequency antenna to an eiiicient height. The structure I l, if metallic, would normally have currents inducedA therein by the radiator 2, as well as by the radiators I and 3. These which: Fig. 1 .schematically shows an yantenna.

system for broadcasting programs at two different frequencies, and Fig. 2 shows another .em-

bodiment of my invention.

'Referring tofFig. `1, there vis shown a plurality of vertical radiators I, 2' and 3 supported on base insulators 4, 5 and B respectively. There maybe any number of such radiators, and broadcast 'stations today commonly use between two and five such radiators. The radiators are generally steel towers between one quarter and five eighths-wave -length in height, although other heights are Vsometimes used. The steel towers are often self-supporting, butin some cases are provided withguy wires. A'I'he antenna .array is excited by a network of transmission lines lo kconnecting thev` are. usually includedxto obtain'theV desired radicurrents in the structure vII.A would valter tlie radiation pattern in a .way which is verypdiiicult to predict.l In order to obviate or reduce this alternation in the radiation pattern, I. provide the following means: A transformer I6 is connected across the insulators I 3 and part of the medium radio frequency energyfed to the antennas l, v2 and'BiS-.alsof'impressed on transformer I6. VThe voltageslf'iinpressed on transformer I6 by transmission line I8 are controlled in phase and amplitude-bylsuitable means Il, well-known in the art. A--'I`fhe -voltages impressed on transformer IS are adjusted so that the induced currents in the structure l' I- lare counterbalanced and reduced to a low value, so that the radiation from the structure is negligible compared with that of the rest of the radiator.- `A coupling lI9 at some point along the structure II connected to .a meter r2l) is used `to indicate whether the'phase and amplitude adjustingv means Il is set to a proper value. The meter 2l) may be adjacent the tower structure Il, or maybe at ground level. It is evident that morev than one coupling circuit I9 and meter 20, suitably spaced along the metallic. structure I-I, may be used.

In Fig. y2 is-shown another-embodiment ofmy invention. This ligure also shows a three-tower array consisting of antennasv 2I, 22 `and-23 mounted on base insulators 24, 25and 26. The antennas 2l, 22 and 23 maybefsteel towers. -The antennas 2I, 22 and 23 are connected tofarbroadcast transmitter through phase and amplitude controllers 2l, 28 and 29 by a transmission'line 30. Atop f the vsteel tower 22 are .insulators-3.3, on which is mounted steel tower structurefl. An impedance 32 is connected across the .insulators 33. The impedance 32 is connected to the medium frequency transmitter by a transmission line 34 and phase and amplitude controller 35.

At or near the top of the metallic structure 3l is mounted a very high frequency antenna 33 for FM or television broadcasting. Antenna 36 is connected to a transmitter by a transmission line 31 of any suitable type, here shown as a two wire cable having a shield 33. The shield 38 may be the common cable braid, a conduit, or it may take other conventional forms. At a quarter wave length of the medium frequency above ground the shield 33 has a connection 39to the tower 22. The shield 38 may be in contact or close proximity to the tower 22 from the connection 39 to the insulator 33. At a quarter vwave length of the medium frequency above the insulator 33, the shield 38 is connected to the structure 3l by the connection 4B.

.. While it ispreferred to space the connections 39 and 40 a quarter wave length above ground and the insulator 33, respectively, it will be understood that the spacing could be any odd number of quarter wave lengths.

' The shield 33 and the tower 22 form a shorted quarter wave length transmission across insulator 25. by virtue of the connection 39, and consequently present a high impedance across insulator 25. Similarly, the structure 3i and the shield 38v present a high impedance across insu- 'latcr 33. Thus, the feeding of the very high frequency antenna 38 is accomplished without introducing low impedances between the tower 22 and ground orthe tower 22 andthe structure 3l.

While the structures Il and 3l may have any suitable length, I prefer to make the length other .thana half wave length of the medium frequency, since it is more difficult to reduce the induced current in4 a half wave length structure than in structures of other lengths.

' Methods other than those I have shown of impressing potentials on the structures H and 3l may be used, a number of such other methods being disclosed in my Patents 2,283,617, 2,283,618

g and 2,283,619.

The Vhigh frequency antennas l2 and 33 are shown`schematically. In practice, these antennas take various forms.` One form of high frequency antenna consists of a plurality of superimposed single turn loops each lying in a horizontal plane.

' The high frequency antennas l2 and 36 may be supported by any desired structure mounted on or integral with structures i I and 3 l.

Iclaim:

1. A radio antenna array comprising a plurality of vertical radiators, a vertical conductive structure mounted on one of said radiators and insulated therefrom, a very high frequency antenna mounted on said vertical conductive structure, means for energizing said very high frequency antenna, means for applying relatively low fre- Y quency voltages to each of said vertical radiators and to said conductive structure, and means for adjusting the relative phases and amplitudes of the voltages applied to said vertical radiators and tosaid conductive structure so as to obtain a desired radiation pattern, and so as to reduce to substantially zero current flow in said conductive structure at said low frequency.

' 2. A radio antenna array comprising a plurality of vertical radiators, a vertical conductive structure insulatedly mounted on one of said radiators as an extension thereof, a very high frequency antenna mounted on said conductive structure, means for energizing said very high frequency antenna, means for impressing relatively low frequency voltages on each of said vertical radiators and on said conductive structure, means for adjusting the phases and amplitudes of said voltages impressed on each of said vertical radiators to obtain a desired radiation pattern, and means for adjusting the phase and amplitude of the voltage impressed on said conductive structure to reduce the relatively low frequency currents induced in said conductive structure bysaid vertical radiators.

3. A radio antenna system comprising an array of antenna towers each insulated from ground, a tall metallic structure mounted on one of said towers, an insulator between said metallic structure and the tower on whichit is mounted, a high frequencyV antenna mounted Vatop said metallic structure, means for energizing said high frequency antenna, means for impressing medium frequency voltages on each of said antenna towers to effect current ow therein, means for impressing a medium frequency voltage between saidmetallic structure and said one of said towers,`and means for adjusting the phase and amplitude of said last named voltage so as to reduce the medium frequency currents induced in said tall metallic structure by current flow in said antenna towers, and means for indicating the current flowing in said metallic structure. i

4. A radio antenna system comprising an array of antenna towers, each insulated from ground," a tall conductive structure mounted on one of said towers, an insulator between said conductive structure and the tower on which it is mounted, a high frequency antenna mounted atop said conductive structure, means for energizing said high frequency antenna, means for impressing relatively low frequency voltages on each of said antenna towers, means for impressing a relatively low frequency Voltage between said conductive structure and said one of said towers, and means for adjusting the phase and amplitude of said last mentioned voltage in such mode as tore'duce relatively low frequency currents induced in said conductive structure by said array.

5. VA radio antenna system comprising an array of antenna towers, each insulated from ground, means for energizing said array by relatively low frequency voltages, a metallic structure mounted on one of said towers, an insulator between said metallic structure and the tower on which'it is mounted, a high frequency antenna mounted atop said tall metallic structure, a transmission line coupled with said high 'frequency antenna and extending adjacent said tall vmetallic structure and the tower on which it is mounted, a metallic shield encompassing said transmission line, means for grounding one end of said shield, means connecting said shield to said last mentioned tower at a point substantially a quarter wave length of said relatively low frequency above ground, means for impressing said relatively low frequency voltage on said metallic structure, and means for adjusting the phase and amplitude of said voltage impressed on said metallic structure to reducethe currents induced therein by currents flowing in said array in response to said relatively low frequency voltages.

6. The apparatus described in claim 5, including, means for connecting said shield to said Y metallic structure at a point substantially a quarlLl giisaidfverticalradiators to:- radiateiafpredeter- "minedispace patterrifof radiof-frequency energy, affurther Vantennaf meansfcomprising fa' conduc- *tfve tower foi-supporting l"sa'i'dCf-'u' ther antenna verticai 'iradiatorsgand meansilfor y reducingy current new in *saidJ condllclfive "tower- -at *diej-,frequency of' said :errer-gy for reducing distcc'tic'1r-o-fv said predetermined space pattern occurring ,in response to currents induced in said-conductive tower by said antenna 1' array.

8. A radio antenna array comprising a plurality of.r verticalz. radiators, means. :for energizing said Vertical radiators to radiate a predetering a plurality of relatively space positioned vertical radiating elementageach of said-radiating elements comprisinga vertical ground supported metallic frame structure, means comprising a source of radio frequency energy for energizing said vertical radiating elements in predetermined relative phase and amplitude to establish a predetermined radiation pattern of radio frequency energy, means comprising a metallic antenna mast insulatedly supported by at least one of said vertical radiating elements and having a current distribution therein in response to said radiation pattern of radio frequency energy, and means for minimizing said current distribution by introducing an opposing current distribution in said metallic mast, said last named means comprising said source of radio frequency energy and means comprising a phase and amplitude controller for coupling said source of radio frequency energy with said metallic antenna mast.

10. A radio frequency antenna system comprising a plurality of relatively space positioned vertical radiating elements, each of said radiating elements comprising a vertical ground supported metallic frame structure, means comprising a source of radio frequency energy for energizing said vertical radiating elements in predetermined relative phase and amplitude to establish a predetermined radiation pattern of radio frequency energy, means comprising a metallic antenna f mast insulatedly supported by at least one of said vertical radiating elements and having a current distribution therein in response to said radiation pattern of radio frequency energy, and means for minimizing said current distribution by introducing an opposing current distribution in said metallic mast, said last named means comprising said source of radio frequency energy, and means comprising a phase and amplitude controller for coupling said source of radio frequency energy with said metallic antenna mast, a metallic linear member extending for substantially the entire length of said metallic mast and of said at least one of said vertical radiating elements and supported thereby, means for electrically connecting said linear member to said at least one of said vertical radiating elements at at least one point adapted to establish a high impedance circuit as seen adjacent ground for said at least one of said vertical radiating elements andfsaid--zmetallic :linea-r" elem'eri.

consideredas' ai resonant itransmissio'ni lin v-groumiimeansforfenergizingsaid :vertical radiavtors; to radiate!:predeterminedspacepattemfof @aims tween said :conductive-tower and saidf'oneor :said

vertical radiaters.A vvoltages of- `adjustablephase and' ampiiltudederived-rrcm'saidmeansffcr energi'zing saidvertical radiators. l

I2. .A radio-antenna arr-ay vc'cmn-lzvrisirigV afplurality-'fot verticalV `radiators eachrfinsula ground byinsulating means, means for-fe l i ingv said :vertical radiators to A'-ra'cuate #a predeterminedf space pai-,tern f-""radiof vfrequency energy, af-urther antenna,- means for Vsup'ierting said :further-antenna fon one or'sai'd -fvertical -radiatorslcomprisingfa conductive tower cally isolatedrf'rom said foneof 's'aidl vertical "radiators by insulating means, and means for substantially reducing distortion of said predetermined space pattern in response to currents induced in said conductive tower by said antenna array comprising circuit means for applying between said conductive tower and said one of said vertical radiators voltages of adjustable phase and amplitude derived from said means for energizing said vertical radiators, means for applying energy to said further antenna comprising a transmission line having a shield supported vat least in part by said conductive tower, and means for preventing short circuiting of said insulating means by said shield comprising conductive connections between said shield and said conductive tower and between said shield and said one of said vertical radiators, said conductive connections being located along said shield at points adapted to establish high impedance circuits as seen across said insulating means for the frequency of said radio frequency energy.

13. A radio antenna array comprising a plurality of vertical radiators, a vertical conductive structure insulatedly mounted on one of said radiators as an extension thereof, means for lmpressing relatively low frequency voltages on each of said Vertical radiators and on said conductive structure, means for adjusting the phases and amplitudes of said voltages impressed on each of said vertical radiators to obtain a desired radiation pattern, and means for adjusting the phase and amplitude of the voltage impressed on said conductive structure so as to reduce the currents inducted in said conductive structure by said vertical radiators.

14. A radio antenna system comprising an array of antenna towers each insulated from ground, a tall metallic structure mounted on one of said towers, an insulator between said metallic structure and the tower on which it is mounted, means for impressing alternating current voltages on each of said antenna towers to effect current iiow therein, means for impressing a further alternating current voltage at the frequency of said first mentioned voltages between said metallic structure and said one of said towers, and means for adjusting the phase and amplitude of said last mentioned voltage so as to reduce the magnitude of current induced in said tall metallic structure by current flow in said antenna towers.

15. A radio antenna system comprising at least -one .vertical radiator insulated from ground,

meansfor venergizing said vertical radiator to radiate a predetermined space pattern of radio frequency energy, a further antenna, means for supporting said Vfurther antenna on one of said vertical radiators comprising a conductive tower electrically isolated from said one of said vertical radiators by insulating means, and means for :substantially reducing distortion of said predetermined space pattern in response to currents induced in saidconductive towerbysaidantenna array comprising circuitmeans for applying between said conductive tower and said one of said vertical radiators voltages of adjustable phase and amplitude derived from said means for energiz- Y ing said vertical radiators, a ground located radio equipment, means for interconnecting said further antenna and said ground located radio equipment comprising a transmission line having a shield supported at least in part by said conductive tower, and means for preventing short circuiting to said radio frequency energy of said insulating means by said shield comprising conductive connections between said shield and said conductive tower and between said shield and said one of said vertical radiators, said conductive connections being located along said shield at points adapted to establish high impedance as seen across said insulating means for the frequency of said radio frequency energy.

RAYMOND M. WILMOT'IE.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS 

